Abstract
We have investigated the feasibility of using a set of multiple MOSFETs in conjunction with the mobileMOSFET wireless dosimetry system, to perform a comprehensive and efficient quality assurance (QA) of IMRT plans. Anatomy specific MOSFET configurations incorporating 5 MOSFETs have been developed for a specially designed IMRT dosimetry phantom. Kilovoltage cone beam computed tomography (kV CBCT) imaging was used to increase the positional precision and accuracy of the detectors and phantom, and so minimize dosimetric uncertainties in high dose gradient regions. The effectiveness of the MOSFET based dose measurements was evaluated by comparing the corresponding doses measured by an ion chamber. For 20 head and neck IMRT plans the agreement between the MOSFET and ionization chamber dose measurements was found to be within −0.26±0.88% and 0.06±1.94% (1σ) for measurement points in the high dose and low dose respectively. A precision of 1 mm in detector positioning was achieved by using the X‐Ray Volume Imaging (XVI) kV CBCT system available with the Elekta Synergy Linear Accelerator. Using the anatomy specific MOSFET configurations, simultaneous measurements were made at five strategically located points covering high dose and low dose regions. The agreement between measurements and calculated doses by the treatment planning system for head and neck and prostate IMRT plans was found to be within 0.47±2.45%. The results indicate that a cylindrical phantom incorporating multiple MOSFET detectors arranged in an anatomy specific configuration, in conjunction with image guidance, can be utilized to perform a comprehensive and efficient quality assurance of IMRT plans.PACS number: 87.55.Qr
Highlights
Field, fluence maps are captured by films or electronic portal imaging devices (EPID) and compared with those calculated by the treatment planning system (TPS)
We have investigated the use of multiple MOSFET (Metal-Oxide Semiconductor Field-Effect Transistor) sensors in conjunction with the mobileMOSFET system (Best Medical Canada, Ottawa, ON) to perform efficient and comprehensive dose measurements for Intensity modulated radiation therapy (IMRT) plan verification
In this report we describe our experience with anatomy specific MOSFET configurations for IMRT plan verification, positioned in the treatment field using image guidance
Summary
70 Amin et al.: Image guided IMRT dosimetry with MOSFET field, fluence maps are captured by films or electronic portal imaging devices (EPID) and compared with those calculated by the treatment planning system (TPS). Point dose measurements with ion chambers are inefficient, requiring a number of steps: (a) calculation of the dose distribution in the phantom data set by importing the IM treatment fields from the patient’s IMRT plan (b) careful selection of measurement points in areas of low dose gradient (c) calculation of the mean dose for the ion chamber volume, and (d) setting up the phantom and ion chamber on the treatment machine and performing the measurements. On the other hand, having simultaneous multiple ion-chambers will perturb the dose distribution For treatment sites such as head and neck, where many critical organs may be present around the target volume, two or more point dose measurements may be required, and require substantial amount of additional time and resources. The volume averaging effect[8] of an ion chamber may introduce significant uncertainties if the measurement point is not within a low dose gradient region
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